1. Field of the Invention
The present invention relates to a method of cutting a hollow and elongate material which is made of a metal such as aluminum and is used to manufacture for example knuckles or the like automobile parts, or to manufacture cylinders or the like large-sized profile parts.
2. Prior Art
The classic sawing, the plasma-arc cutting and the like technique have been employed to slice for example an aluminum hollow extrusion, especially an extrusion of a large-diameter extrusion.
It is however noted that the a saw for the cutting of such a material is applied to a considerably large peripheral zone, and it is somewhat difficult to treat with swarf.
The plasma-arc cutting is also applied to a large peripheral zone, and lowers the mechanical strength of an adjacent portion due to a high temperature. Further, a considerable amount of mud is produced from the portion cut in this way and sticks to the inner surface of the hollow material, also making it difficult to remove the mud.
Therefore, the laser cutting of those materials has been studied and proposed because it is free from the described various drawbacks.
Generally and in nature, a laser energy for cutting the material is restricted only to a pin point where the laser beam is focused and possibly to a very narrow region adjacent to the pin point. In a case wherein a large-diameter hollow extrusion has to be sliced by the laser cutting method, the laser beam will be applied from the outside and onto a peripheral portion in a transverse direction. Another peripheral portion located opposite to the first mentioned portion in a diametrical direction cannot receive any effective amount of the laser energy, so that the extrusion is not sliced completely in a satisfactory manner. Thus, the laser cutting has been deemed to be a method improper to slice such a hollow material of a comparatively large size.